108 



PROTECTION OF POLLEN. 



higher temperature than would otherwise have been the case. This explanation 

 must be borne in mind. 



We find, therefore, an amount of variety in the forms of safeguard against 



wet corresponding to the multiplicity of the adaptations which subserve the 



purpose of pollen-transport by the wind or by butterflies, bees, beetles, or flies, 



as the case may be. The means of protection are diversified also according to 



whether the cover is placed immediately over the pollen or over an entire group 



of flowers, whether it shelters the newly-opened, pollen-laden anthers or that part 



of the flower whereon pollen liberated from the anthers is temporarily deposited; 



and again they vary according as it is the anther-walls, stigmas, petals, involucre, 



or foliage-leaves which have to serve as roof to the pollen^ The Lime-tree affords 



an instance of the last-mentioned arrangement, its flowers being invariably so 



placed that at the time when pollen is yielded by the anthers they are covered 



by the broad, flat foliage-leaves. However sharp the showers to which a Lime-tree 



is subjected the rain-drops roll off" the blades of the leaves, and it is only by 



exception that any one of the many flowers stationed beneath them is wetted. 



The same provision is met with in a few species of Dcqjhne (e.g. D. Laureola and 



D. Philijjpi), in several Malvaceae (e.g. Altlma pallida and A. rosea), and in the 



Impatiens Nolitangere, a plant which possesses other remarkable features and 



will be the subject of further discussion by and by (c/. fig. 220 '). In Impatiens 



the flower-buds are held by their delicate stalks above the surfaces of the leaves 



from whose axils they spring, and the leaves are at first folded upwards like 



erect troughs. Subsequently, when the buds get bigger and their stalks longer, 



the latter slip down to one side of the leaves and hide beneath them, whilst the 



leaf-margins still continue to be curved upward. The leaf then flattens itself out 



and fixes the drooping flower-stalk by means of one of the lobes of its heart-shaped 



base, and thus indirectly keeps the suspended bud in position, so that when later 



on the bud and its anthers open, which they do simultaneously, they are roofed 



over by a smooth lamina, off" which the rain-drops roll without ever wetting the 



flowers or their pollen (fig. 220 ^). 



In many Aroidcc-B the spadix is completely covered by the large sheathing 

 leaf or spathe at the time when the anthers burst, as, for instance, in the curious 

 Japanese Arisema ringens, where the spathe curves over the inflorescence like 

 a Phrygian cap, and in Ariojysis peltata, where the spadix is protected from rain 

 and dew by a sheathing leaf resembling a boat with the keel uppermost' (c/. 

 fig. 221^). Genetyllis tulipifera, a shrub belonging to the Myrtacete, bears at 

 the ends of slender, woody twigs inflorescences which at first sight might be 

 taken to be pendent tulips. On closer inspection it appears that the large white 

 leaves with red veins which recall the leaves of the tulip perianth are involucral 

 bracts which cover the closely-crowded flowers and shield them from the rain. 

 Similarly in the case of the Banana and its allies {Musa, Ravenala) the flowers 

 are covered over when the pollen is mature by large involucral sheaths which 

 subsequently, after the pollen has been used up and there is no longer any need 



